1. Field of the Invention:
The present invention relates to a system for detecting data spectrum distortion in transmission, e.g. distortions caused by selective fading and, more particularly, to a system for detecting possible in-band dispersions, wherein dispersion means an amplitude dispersion.
2. Description of the Related Art:
Until today, the measurement of amplitude dispersion has been made by measuring the power of the data spectrum around `n` frequencies; generally this measurement is carried out by `n` frequency selective filters.
The obtained information is much more complete as `n` increases; but this functional requirement conflicts with many other requirements, in particular the complexity involved in manufacturing frequency selective filters (band-pass filters, with a very narrow bandwidth) and, with the need to save space and to limit costs. Owing to these and other requirements, the number `n` of filters that are used is typically limited to two or three.
If two filters are used, or in any case in which if `n` is an even number, information regarding the dissymmetry of the data spectrum with respect to central frequency (fc) is, obtained, which is in any event, incomplete, as the channel bandwidth is sampled only in some points; hence the information is not "all band".
If there are three filters, or in any case in which `n` is an odd number, it is possible to detect also the presence of fading with notch frequency equal to the frequency of the central band, but also in this case there is still the inconvenience of obtaining a measurement which not extended over the whole band.